1. Field of the Invention
The present invention relates to a method of controlling a treatment apparatus and, more particularly, to a method of controlling a treatment apparatus for treating an object to be treated in a low-temperature atmosphere.
2. Description of the Related Art
In a technique, such as a dry etching technique, in which a plasma is generated by using a reactive gas and an object to be treated is treated with this plasma, the object to be treated, such as a semiconductor wafer, is etched while it is cooled in a low-temperature atmosphere, in order to perform etching in a direction perpendicular to the surface of the object to be treated and obtain a high selectivity. In this case, a low-temperature treatment technique using a cooling mechanism is employed. In this mechanism, a cooling medium container is formed in a mounting table for mounting an object to be treated, and a cooling medium is externally supplied to the cooling medium container to cool the object to be treated by the resultant heat transfer, thereby decreasing the temperature of the reaction surface of the object.
In a treatment apparatus for performing the low-temperature treatment as mentioned above, individual members are constituted not by a single material, such as aluminum, but by several different types of materials in accordance with the performance required for each member, e.g., electrical insulating properties, heat insulating properties, strength, and low-temperature resistance. Additionally, depending on the type of a treatment apparatus, different materials must be airtightly joined so that neither a gas nor a liquid leaks. In this case, several different joining techniques are selectively used in accordance with the types of materials to be joined. For example, a friction welding method is used in airtightly joining an aluminum member to a stainless steel member, an electron beam welding method is used in airtightly joining a stainless steel member to a Kovar member, and a vacuum brazing method is used in airtightly joining a ceramic member to a Kovar member.
None of the above joining techniques, however, is perfect. Therefore, if even a slight gap is present in a connected portion between members constituting a treatment apparatus, moisture in the treatment apparatus enters through this gap by, e.g., a capillary phenomenon. Since the treatment apparatus is exposed to a severe atmosphere, such as an ultra-low-temperature atmosphere, during a treatment, the moisture entering the gap in the joint portion freezes during the treatment. The treatment apparatus, on the other hand, is heated up to room temperature after the treatment, so the ice defrosts into water again. If the moisture repeatedly freezes and defrosts in the gap, the gap is widened by volume expansion during the freezing. Consequently, the gap may produce cracks in the connected portion or in the constituting members, even if the gap is initially very narrow. If cracks are formed in the connected portion or in the constituting members, a cooling medium, such as liquid nitrogen, leaks out from that portion (a cold-leak phenomenon) to vary the internal pressure of the treatment apparatus. This degrades not only the cooling function but also the function of the overall treatment apparatus. In extreme cases, the treatment apparatus fails or is broken.
Furthermore, many portions of the cooling mechanism provided in the treatment apparatus are exposed to the outer atmosphere, so it is impossible to avoid an intake of external heat, i.e., a temperature rise caused by circulation of a cooling medium. This consequently degrades the cooling function to make a stable low-temperature treatment impossible. For this reason, it is necessary to minimize the intake of external heat in the cooling mechanism.